The purpose of the study was to determine width, depth, length, duration and microrelief location of seasonal crack openings in a Vertisol during a 10 year period beginning in 1989. The actual crack width and depth measurements would also allow us to evaluate the current method of using climate data to determine Ustic and Udic suborders of Vertisols in Texas. A 100 m2 study area was located in a native prairie of Laewest clay (Typic Hapludert) in the Texas Gulf Coast Prairie, south of Victoria, Texas. Width and length of cracks were measured with 1 cm and 5 cm accuracy respectively in the field and plotted to scale on engineer graph paper. Crack depth and inside width were measured at selected points with a 2 m long steel tape with a 1 cm thick tip (crackometer) for 1989-1992 and a similar steel tape with a 0.5 cm thick tip for 1993-1998. Precipitation and seasonal high water tables were recorded, and soil moisture samples at four depths to 1 m deep were periodically taken during the study. The crack diagrams were digitized using a GIS program, and crack dimensions such as length, width, depth and volume were calculated. The temporal and spatial crack data were evaluated according to soil moisture and local weather observations (including precipitation measurements). Primary crack opening and closing cycles were quantified. These cracking events will be discussed as they relate to Soil Taxonomy and classification of Vertisols.
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